Light general-aviation airplanes can be categorized into high-wing and low-wing monoplane types. Because the wings of the latter type provide a conveniently positioned structure for securing the main undercarriage gear to the aircraft, the same hydraulic shock absorber undercarriage arrangement in conventional use in large commercial aircraft can be adopted. For the popular high-wing types however such a conveniently positioned structure is absent.
For larger high-wing aircraft a short outrigger or sponson is provided to which the main gear is secured and which is often used to hold auxiliary fuel. For light high-wing aircraft such a structural outrigging would add additional weight and complexity. Instead such high-wing aircraft utilize a simple flat-spring undercarriage arrangement.
Accordingly, the single-leaf flat-spring main undercarriage gear has been the mainstay of the light high-wing aircraft industry for perhaps a half century. Originally constructed of spring steel, the considerable weight of the metal spring partially diminished the advantages in simplicity of this undercarriage arrangement over the far more complex hydraulic system. However, the development of light glass-fibre reinforced polymer flat-springs has eliminated this disability.
Helicopters, like high-wing monoplanes, do not have a conveniently positioned structure onto which the main undercarriage gear can be secured. In the case of the larger helicopters, like the larger high-wing aircraft, a sponson is provided. Lighter helicopters use a skid arrangement which provides stability and simplicity, but at the price of considerable inconvenience. Provisions must be made for auxiliary wheels that must be manually installed on the skids for ground handling.
For light helicopter operators who would prefer a wheeled undercarriage, the flat-spring arrangement would appear ideal in terms of both weight and simplicity. However, for the flat-springs to properly absorb the shock of landing, the aircraft must be rolling on contact with the ground to allow the flat-springs to deflect. Because helicopters generally land from a hover with essentially no forward motion, flat-springs can not deflect to absorb the landing load. The objective of the undercarriage apparatus for vertical-lift aircraft disclosed herein is to provide an apparatus to remedy this limitation of the flat-spring undercarriage arrangement.